1. Field of the Invention
The present invention relates to methods for controlling the release of agricultural active ingredients from treated plant seeds, and more particularly to methods for controlling the release of agricultural active ingredients from treated plant seeds by the use of seed coatings.
2. Description of Related Art
The development and use of pesticides has increased the yield of most agronomically important plants. Pesticides, including herbicides, insecticides, nematocides, acaracides, fungicides, bactericides, and the like, are now widely applied to soils prior to, during, or after seed planting, or are applied directly or indirectly to growing plants at various times during the growing season.
Widespread use of pesticides has not been without problems, however, due to the wide spectrum of activity and high toxicity of some pesticides. Such negative results have been exacerbated by the widespread distribution of pesticides in the environment through such vectors as runoff, wind-drift, leaching, animal activity and the like. This type of movement of pesticides away their point of application and target of activity also requires that higher levels of the pesticide be used in order to insure that the application provides the desired pesticidal activity for the desired period of time that it is required.
One method that has been found to be promising in some applications is the treatment of plant seeds with pesticides. General information on this subject is provided in, for example, Chemtech, 8.284-287 (May 1978). In situations where seed treatment is effective, it can reduce the amount of pesticide that is required to obtain a desired level of activity. Other advantages of direct, pre-planting seed treatment include reducing the number of separate field passes that a farmer must make to prepare for, plant, and raise a crop, and limiting at least the initial zone of pesticidal activity to the seed and its immediate environment. Further information about seed coatings has been published by Barke et al., who describe seed coating compositions comprising a stabilizing polyol in U.S. Pat. No. 4,272,417. Seed coatings containing polyelectrolyte complexes are disclosed by Dannelly in U.S. Pat. No. 4,245,432. Kouno has described a method of applying gel coating to seeds in U.S. Pat. No. 4,808,430. In U.S. Pat. No. 4,735,015, Schmolka has described enveloping a seed in a coating containing certain polyoxyethylene-polyoxybutylene block copolymers.
Early seed treatment applications were often carried out by simply applying a pesticide—a fungicide, for example—directly to a seed, followed by drying the treated seed for storage and use. It was soon apparent, however, that this technique also had drawbacks, such as toxicity of the pesticide to the seed, high rates of loss of the pesticide during storage and the exposure of workers handling and planting the seed to high levels of the pesticide. In cases where the pesticide was water soluble or easily leached from the seed, the loss of pesticide from the zone of the seed could be rapid. Not only could this reduce the efficacy of the treatment, but could also cause unwanted release of the pesticide into the environment.
In many cases, it is desirable to retard or control the release of the active from the seed because of safety considerations and to increase the efficiency of use of the active. For example, if release of a pesticide can be controlled so that the concentration of the pesticide in the zone of the seed reaches and remains at an effective level during the time the target pest is active, the efficiency of use of the pesticide is increased over what would ordinarily be expected if the pesticide was merely applied to the soil at planting. Examples of methods to control the release of actives by the use of seed coatings have been described by, among others, Turnblad et al. in U.S. Pat. Nos. 5,849,320 and 5,876,739, who disclosed insecticidal coatings comprising a polymer binder, an insecticide and a filler, where the binder formed a matrix for the insecticide and the filler. Application of such a coating to a seed and the optional subsequent application of a protective polymer overcoating were also described.
One of the considerations of including a pesticide, such as an insecticide, in the seed coating itself is that the active agent is present throughout the coating and even on the outer surface of the coated seed. This permits anyone handling the seed to contact the active ingredient directly. In order to minimize this contact, it is necessary to add a second, additional, coating to the seed. This requires additional materials and results in higher cost of seed preparation.
Another problem that has hindered the development of seed coatings that control the release of pesticides has been the requirement for coatings that are carefully tailored to provide a certain chemical relationship with the pesticide. For example, the combination of the pesticide and the coating must meet certain criteria of release rate, protection of the active, protection of the seed, and the like, while not binding the pesticide so tightly that release is prevented entirely. The development of coating formulations that meet these criteria has routinely taken significant time and effort, and the formulations are most often limited to use with one type of pesticide.
Accordingly, it would be useful to devise a method for controlling the release of agricultural actives from a seed that has been treated with such actives where the methods are easy, fast and economical to administer, and are effective in controlling the release of the active from the treated seed. Moreover, it would be useful if such methods could be used with a wide range of agricultural actives and if they could be practiced without the inconvenience and expense of having to develop a polymer coating having certain chemical compatibility between a particular active and the polymer.